Wearable electronic devices have gained popularity among consumers. A wearable electronic device may track user's activities using a variety of sensors and help the user to maintain a healthy life style. In order to determine a user's activities, a wearable electronic device collects activity data and runs computations on that data. It may be desirable to provide a wearable electronic device that is configured to accurately monitor, detect, and characterize (or classify) the motion of the human body based on the motion of the device in real-time and with low power consumption.